The attached FIGS. 1 and 2 depict a cascade-type thrust reverser of the prior art, in the direct-jet position.
As is known per se, a thrust reverser such as this comprises:                a fixed structure 1 on which a rear frame 3 supporting said cascades of vanes 5 is mounted,        a mobile structure 7 comprising an outer wall 9, an inner wall 11 formed in part by at least one acoustic panel 13, and at least one partition 15 connecting said outer wall 9 to said acoustic panel 13, and        actuators 16 interposed between said fixed structure 1 and said mobile structure 7, extending through orifices 17, 19 formed in said rear frame 3 and said partition 15 respectively.        
FIG. 2 depicts the thrust reverser in the direct-jet configuration.
In this configuration, air from upstream of the thrust reverser, that is to say from the left in FIG. 2, flows along the flow path 21 situated between the mobile structure 7 and an inner fixed structure 23 in the downstream direction of the thrust reverser, that is to say to the right in FIG. 2, as indicated by the arrow F1.
Link rods 25 connect mobile panels 27, situated facing the cascades of vanes 5 and articulated to the mobile structure 7, to the inner fixed structure 23.
The switch from the direct-jet configuration to the indirect-jet configuration (not depicted) is performed by extending the actuators 16.
Under the effect of this extending, the link rods 25 pull the mobile panels 23 across the airflow path 21, causing air flowing along the flow path 21 to be deflected toward the outside and toward the upstream end of the thrust reverser, as indicated by the arrow F2, thus generating a reverse thrust that contributes to the braking of an aircraft that is attempting to land.
In practice, and notably for aerodynamic optimization reasons, it is appropriate for the radial thickness of the mobile structure 7 in the region of the cascades of vanes 5 to be as small as possible; this is particularly critical in the case of large nacelles, such as those intended for the engines of the Airbus A380.
Now, this reduction in thickness is limited notably by the radial thickness of the rear frame 3 and by a minimum radial distance d between this rear frame and the acoustic panel 13.
The radial thickness of the rear frame 3 cannot drop below a threshold value without carrying the risk of dangerously weakening the entire thrust reverser, and the minimum distance d ensures that the acoustic panel 13 does not come into contact with the rear frame.
It will therefore be appreciated that, in a conventional cascade-type thrust reverser, the radial thickness of the mobile part 7 in the region of the cascades of vanes, cannot drop below a certain threshold value.